A preliminary investigation of the effects of soil electromagnetic properties on metal detectors

Abstract

Some soils can adversely affect the operation of sensitive metal detectors widely used to detect buried landmines. Although there has been some related work in geophysics, researchers in metal detection techniques, until very recently, seem to have largely ignored the issue of problem soil. As a result, rigorous scientific investigations of how soil electromagnetic properties may affect the operation of metal detectors are lacking. Thus, there is a need for theoretical and experimental studies to clarify which electromagnetic properties are important and to what extent they affect the performance of metal detectors of various designs. The paper presents a systematic analytical framework, based on existing work in geophysics and non-destructive testing, for studying the effects of soil electromagnetic properties on the functioning of metal detectors. For this initial study the burial medium is modelled as a half-space. While soil electrical conductivity has been assumed to be real and independent of frequency, soil magnetic susceptibility has been modelled as complex and frequency dependent. Simplified versions of the analysis techniques have been applied to three selected cases of practical importance, namely, non-conducting soil with constant susceptibility, non-conducting soil with frequency-dependent susceptibility and non-magnetic soil with constant conductivity. Results from a preliminary analysis of even these simple cases explain a number of previous experimental observations, for example, the greater influence of magnetic properties than of electrical conductivity on the performance of metal detectors.

Inversion of soil's and immersed objects's electromagnetic parameters symultaneously

“…Although it is recognized that, in practice, the spatial inhomogeneity of soil electromagnetic properties may be the limiting factor in the performance of the metal detector, for this study the soil is modeled as a homogeneous half-space. Direct problem is solved basing on field representation described in [7]. The results of inversion procedure are depicted on fig.1.…”

Influence of dispersive soil electromagnetic properties on hand‐held time domain electromagnetic sensors

“…As Das (2004) has demonstrated, a useful approximation for the response over a nonconductive, dispersive magnetic soil is obtained by generalizing the previous result for a frequencydependent magnetic susceptibility. In particular, a well estab-1 In theory (equations (12) and (20)), the associated primary step response ν p (t) = −μ 0 πa 2 Iδ(t) ∞ 0 [J 1 (λa)] 2 dλ is similarly impulsive and infinite for coincident coils and independent of stand-off (h).…”

Electromagnetic induction response of a target buried in conductive and magnetic soil

“…One of the other important factors that can influence this signal is the host soil. A systematic analytical framework, based on well-established techniques in geophysics and non-destructive testing, for studying the effects of soil electromagnetic properties was presented in a previous paper [7]. Numerical results included in that paper were limited and were used primarily to illustrate the response produced by a soil half-space with specific electromagnetic characteristics and to clearly explain some well-known previous experimental observations.…”

“…Numerical results included in that paper were limited and were used primarily to illustrate the response produced by a soil half-space with specific electromagnetic characteristics and to clearly explain some well-known previous experimental observations. In this paper, based on the formulation previously discussed in [7], the electromagnetic response of a buried small metallic sphere is analyzed and computed. The results are used to investigate the influence that electromagnetic parameters of the host soil have on the signal produced by a target and hence on its detectability by a metal detector.…”